1. Field of the Invention
The present invention relates to a knee protecting airbag device in which an airbag to be expanded and inflated with an inflating gas let in protects the knee of an occupant such as a driver and a front seat passenger.
2. Description of Related Art
As disclosed in Japanese Patent Laid-Open No. Hei 10-315894, the device for protecting the knee of an occupant in the prior art has a case, which houses a folded airbag and an inflator for feeding the airbag with inflation gas, at the lower side of the column cover below the steering column. The opening of the case is closed by an airbag cover. In an airbag device of this kind, there are arranged interior members such as a lower panel of an instrument panel (as will be called “dashboard” hereinafter) around the airbag cover.
Considering the mounting workability of the airbag device on a vehicle, the airbag cover is prepared separately from these interior members. The airbag cover is attached to the case together with the airbag and the inflator to form an airbag assembly. It is desired to mount this airbag assembly on a vehicle utilizing a predetermined portion of the case, from the viewpoint of mounting workability.
When the case is fixed to a predetermined position of the vehicle, however, there may arise an assembling error such as dimensional inconsistency between the airbag cover and the interior members. In this case, an adequate appearance and design cannot be presented because of steps or gaps between the airbag cover and the interior members.
Therefore, it is desired that an airbag assembly is mounted on a vehicle while preventing the assembling error between the airbag cover and the interior members.
On the other hand, another knee protecting airbag device in the prior art has a generally square-plate-shaped door which opens upward turning the lower end thereof upward, as a door to be pushed and opened by an inflating airbag (refer to International Publication No. WO 02/04261 A1).
In the upward-opening door of this kind, it is likely that one of the left and right side edges approaches the occupant whereas the other is apart from the occupant because of the circumferential design. In this case, the leading end of the opened door (or the lower end, before opening) may push the side of the vehicular side wall being a part of the completely inflated airbag toward the vehicle's rear side.
Especially, the upward-opening door largely moves upward by the intense force of the inflating airbag at the initial time of opening. However, the upward-opening door sometimes returns to close right before the completion of the inflation of the airbag. Then, the leading end of the upward-opening door pushes the vehicular side wall of the airbag rearward.
At this time, the following problem may arise if the distance between the upward-opening door and an occupant, before opening, is different at one of the left and right side edge and at the other because of the circumferential design. Specifically, when the upward-opening door pushes the airbag rearward, the leading end of the side edge of the door closer to the occupant pushes the airbag even closer to the occupant, even if the airbag itself is so mounted on the case as to confront head-on the occupant. Accordingly, the expanded and inflated airbag is twisted, instead of confronting head-on the occupant.
As a result, the expanded and inflated airbag does not contact the advancing knee of the occupant properly.
Therefore, it is desired that the expanded and inflated airbag be made confront head-on the occupant in case the knee protecting airbag device has an upward-opening door in which the distances in the longitudinal direction to the occupant are different at the left and right side edges thereof.
In an airbag device of this kind, moreover, an airbag assembly desirably is formed in advance of individual parts and is mounted on a vehicle for facilitating the mounting work.
In this case, the general portion in the airbag cover around the door is surrounded by vehicle's interior members. If this general portion is made greater in its contour, it blocks the fixing work of the case to the body by means of bolts and so on. Accordingly, the fixing work including fastening bolts is made using a mounting hole opened on the general portion. Moreover, a cap for closing the mounting hole is needed so as not to deteriorate the design of the airbag cover after the fixing work.
However, the airbag cover of this kind is so constructed to open by the push of an expanding and inflating airbag, as to protrude the airbag from the opening thereof. That is, the airbag cover receives a rapid pressure from the airbag when the airbag device is activated. Accordingly, the cap has to be attached on the airbag cover so as not to be blown off.
Of course, the cap has to be easily attached on the airbag cover for closing the mounting hole, too.